Ricin is a heterodimeric plant protein that is potently toxic to mammalian cells. Toxicity results from the catalytic depurination of eukaryotic ribo-somes by ricin toxin A chain (RTA) tBáo cáo khoa học: The isolation and characterization of temperature-dependehat follows toxin endocytosis to, and translocation across, the endoplasmic reticulum membrane.